In the south in tight woods with small deer, .223 can be effective. Not ideal, but humane kills can be made. You have to know you have your shot perfect. You have to have a load that will hold together. Deer in the 90-120 lb range are probably the best candidates. If a big old buck walks in I'd probably cuss and pass on the shot.

Indiana corn fed monster deer should have a heavier caliber used, same as some the big mule deer out west.

Yes want more of the 5.56 but yeah I'd be shooting 100ish yards and not huge but sc deer!